Application of the silicon-tether strategy for controlling the regioselectivity and diastereoselectivity of intramolecular nitrone cycloadditions foraminopolyol synthesis

Highly regioselective and diastereoselective intramolecular chiral nitrone cycloaddition reactions with a vinyl group tethered by a silicon atom have been developed as a general method for the synthesis of stereodefined amino polyols. This strategy features a series of one-pot reactions involving (1 ) DIBAH reduction of the carbonyl groups of chiral alpha- or -beta-hydroxy carbonyl compounds, in which the hydroxy group is protected as diphenylviny lsilyl ethers, at -78 degrees C to give an aldehyde, (2) condensation of th e aldehyde with N-benzylhydroxylamine to furnish nitrone (-78 degrees C --> rt), and (3) intramolecular [3 + 2] dipolar cycloaddition reaction between the nitrone and the silicon-tethered vinyl group (rt --> 70 degrees C, 3-1 5 h) to give isoxazolidine derivatives as direct precursors for amino polyo ls. Since the cycloaddition reaction is concerted in nature and passes thro ugh a fused-bicyclic transition state, the substituents, the nitrone substr ate, and the silicon atom bias the stereochemical course of this addition, resulting in highly diastereoselective and synthetically useful transformat ions.